Dipole antenna with dielectric casing

ABSTRACT

Constructions for radio antennae, whose size is made appreciably less than the size of conventional antennae by using the dielectric properties of a powdered mixture of barium titanate and strontium titanate.

United States Patent 11 1 1111 3,924,238

James 1 1 Dec. 2, 1975 DIPOLE ANTENNA WITH DIELECTRIC 2,748,386 5/1956 Polydoroff 343/787 CASING 3,550,145 12/1970 Chen-total 343/830 [75] Inventor: James Roderick James, Swindon,

England Primary E.\'aminerEli Liberman [7}] Assignee, The Plessey Company Limited Attorney, Agent, or FirmScrivener Parker Scrivener Essex, England & Clarke [22] Filed: June 12, 1974 [21] Appl. No.: 478,622 [57] ABSTRACT 52 us. (:1. 343/807- 343/873 Constructions for radio antennae Whose Size is made 1511 Int. H01 1/40 appreciably less than the Size of conventional amen [58] Field of Search 343/754 787 873 807 by using the dielectric Properties of a Powdered q mixture of barium titanate arid strontium titanatei [56] References Cited UNITED STATES PATENTS 1 Claim, 4 Drawing Figures 2,567,260 9/1951 Wiley 343/873 US. Patent Dec. 2, 1975 3,924,238

DIPOLE ANTENNA WITH DIELECTRIC CASING This invention relates to radio antennae with particular but not exclusive reference to antennae suitable for use in the UHF or VHF ranges.

According to the invention there is provided a radio antenna comprising at least one monopole or at least one dipole, and low loss high permittivity dielectric material surrounding each monopole or each dipole, the dielectric material being dimensioned so as to produce resonance at the frequency at which the antenna is to operate.

The invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a cross section of an antenna having one monopole,

FIG. 2 is a cross section of an antenna having one dipole,

FIG. 3 is a cross section of an antenna having three monopoles,

FIG. 4 is a plan view of the antenna of FIG. 3.

In the monopole antenna of FIG. 1, the pole comprises an end 1 of a core 2 of a coaxial cable by which signals are passed to or from the pole. The cable has a sleeve 3 which is joined to a ground plate 4 lying perpendicular to the core 2. The pole 1 is surrounded by dielectric material 5 which is housed inside an annular wall 6. Preferably the dielectric material is a mixture of barium titanate and strontium titanate in powder form.

In the dipole antenna of FIG. 2, each pole comprises a metallic rod 7 to or from which signals are passed over individual conductors 8. The rods 7 and their respective conductors 8 are disposed on opposite faces of a sheet 9 of insulating material, the rods 7 being in alignment with each other. Each rod 7 is surrounded by dielectric material 5 contained in a housing 10.

In the threefold monopole antenna shown in FIGS. 3, 4, the. central monopole is arranged as shown in FIG. 1, and the references of FIG. 1 are used. Two other monopoles 11, 12 are disposed in line with the pole 1, and are connected to the core 2 by wires 13. The pole 11 is shorter than the pole 1 and the pole 12 is longer than the pole l. The poles 11, 1, 12 are surrounded by dielectric material 5, which is housed in a container 14, and presents an inclined surface on account of the differing lengths of the poles. Conveniently the container 14 is made of polyacrylate insulating material.

Conveniently the same material is used for the dielectric material 5 in each of the antennae.

In a variant of the antenna of FIGS. 3, 4, the long monopole 12 may be replaced by a conductive plate or grating lying perpendicular to the axis on which the poles are aligned, as indicated by the broken line 15.

Under these conditions, the broken line 15 may be one of the boundaries of the dielectric material 5.

By using the dielectric material it is possible to make an appreciable reduction in the length of a pole as compared with conventional antennae. The reduction in length is inversely proportional to the square root of the dielectric constant, relative to free space, of the dielectric material. Similar reductions are obtainable with dipole antennae, and in the spacing of poles in antennae having a plurality of spaced poles.

Resonance at the operating; frequency of an antenna can be obtained if the antenna dimensions conform to the equation:

where a, b are the radii of the conductive rod 1, 7 and the surrounding dielectric material 5 respectively, (see FIGS. 1, 2); J J Y,,, y indicate Bessel functions according to accepted mathematical notation; and k is real and equal to k V l(1/x) In evaluating K and x is derived from A0 L rm WY;

E being the relative dielectric constant of the dielectric material; L being the length of a monopole antenna (FIG. 1) or half-length of a dipole antenna (FIG. 2); )to being the free space wave length of radio waves at the desired frequency; and m is an integer.

Practical dimensions, obtained from the foregoing formulae, generally require a dielectric material whose permittivity is at least 4. The term high permittivity used herein, is used to mean permittivities of the value 4 or more.

It is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation in its scope.

What is claimed is:

1. A radio antenna comprising a slab of insulating material having two opposed faces; two aligned conductive rods each perpendicular to one of said faces to form a dipole, a transmission line on opposite faces of the slab connected to the dipole; dielectric material surrounding each rod, and comprising a mixture of barium titanate and strontium titanate in powder form; and a housing whereby said powder is constrained in position around said rods. 

1. A RADIO ANTENNA COMPRISING A SLAB OF INSULATING MATERIAL HAVING TWO OPPOSED FACES; TWO ALIGNED CONDUCTIVE RODS EACH PERPENDICULAR TO ONE OF SAID FACES TO FORM A DIPOLE, A TRANSMISSION LINE ON OPPOSITE FACES OF THE SLAB CONNECTED TO THE DIPOLE; DIELECTRIC MATERIAL SURROUNDING EACH ROD, AND COMPRISING A MIXTURE OF BARIUM TITANATE AND STRONTIUM TITANATE IN POWDER FORM, AND A HOUSING WHEREBY SAID POWDER IS CONSTRAINED IN POSITION AROUND SAID RODS. 